Deal with different floor heights at a doorway

Fit the right threshold trim to level a doorway step safely, whatever floor type is underneath.

DFH-01Measure the height difference and pick your fixLay a straightedge across the doorway and measure the gap down to each floor surface with a tape measure. A few mm needs only a flush strip. Anything from about 5mm to 15mm needs a ramped threshold trim. More than 15mm usually means building up the lower floor or fitting a proper sloped threshold - treat this as a bigger job.

1 each · Tape measure

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1 each · Spirit level or straightedge

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DFH-02Check what's under the floor before you drillSweep a cable and pipe detector across the doorway area, but still assume something could be there - detectors miss deep cables, metal conduit, and pipes outside the usual safe zones. Doorways often have central heating pipe runs or underfloor heating manifolds nearby. Find your stopcock now, usually under the kitchen sink, and check it turns freely. If you have any doubt, isolate the relevant circuit at the consumer unit before drilling, and turn off the water at the stopcock before cutting into anything that could hold a pipe.

1 each · Cable and pipe detector

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DFH-03Choose the right transition trimMatch the trim to the height gap and the two floor types meeting: a flat reducer or self-adhesive strip for small gaps, a single-ramp trim where one side is higher, a double-ramp trim where the doorway sits between two different heights, or a T-bar where floors are level but different finishes. For carpet-to-hard-floor, use a carpet gripper bar instead of a flat trim.

1 each · Aluminium ramp threshold trim

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1 each · Carpet gripper bar (if needed)

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DFH-04Cut the trim to widthMeasure the doorway width between the door linings, not the wall opening. Mark the trim and cut it with a hacksaw or mitre saw, cutting slightly short rather than tight so it doesn't bind against the frame. File any rough cut edges smooth so they don't catch bare feet.

1 each · Hacksaw

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1 each · Metal file

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DFH-05Fix the trim - method depends on the floor underneathOn a timber subfloor (floorboards or chipboard over joists), drill a 2mm pilot hole and drive 3.5 x 25mm wood screws straight in - no plug needed. On a solid concrete or screed floor, drill with a 6mm masonry bit, push in a 6mm wall plug, then drive a 6 x 40mm screw. Sit the trim down firmly and check it doesn't rock before you leave it.

8 each · Wood screws 3.5 x 25mm

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1 each · Masonry drill bit 6mm

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8 each · Wall plugs 6mm

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8 each · Screws for masonry 6 x 40mm

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1 each · Drill driver

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DFH-06Trim the door bottom if it now catchesClose the door and check it clears the new trim by at least a few mm all the way across. If it catches, mark the line, remove the door, and plane or saw a small amount off the bottom evenly. If this is a fire door - common on flats and between a house and an integral garage - do not remove more than the manufacturer allows.

RULES

1 each · Hand plane

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1 each · Panel saw

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KNOW THE RULES

Fire doors must keep their certified gaps under Building Regulations (Approved Document B, fire safety). Check the manufacturer's fitting instructions before trimming a fire door.

DFH-07Finish and tidy upRun a thin bead of silicone sealant under the trim edges if the doorway leads to a kitchen or bathroom, to stop water tracking underneath. Vacuum up dust and offcuts, and check the trim sits flat with no sharp edges or trip points. Open and close the door a few times to make sure it swings freely.

1 each · Silicone sealant

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1 each · Dust sheet

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